Update lpu_parser.py
Merge pull request #2 from kpsychas/patch-1

Fix comment in lpu_parser.py
Utilize the debug flag to output the membrane potential and current in LeakyIAF
remove float casting of edge attributes
change the data type of 'model' attribute to string in four GEXF files.
switch to LPU_rev in sensory_int_demo; use AGG as backend for its visualization
major fixes to LPU_rev; LPU.py can now be phased out once all examples are tested with LPU_rev; see details below.

1. fixed wrong logic in update buffer.
2. make sure _read_external() reads all available input.
3. fixed incorrect assumption of in_gpot_dict and in_spike_dict maintaining the same order as conn_dict.
4. do not execute neu/syn update at the first run step when the LPU is not running by itself.
Add note to intro demo cautioning that certain seed values may produce networks that don't generate any responses.
Update intro notebook to use 'extern' rather than 'input' in neuron params.
Tidy up generic LPU notebook.
Explain purpose of lamina data file 'input' column in lamina notebook.
Make prompt numbers consecutive in multi notebook.
Define other_lpu_map in LPU_rev even in the case
of unconnected LPUs.
Don't need to import random module in gen_generic_lpu.py.
Convert lamina demo to use LPU_rev.py.
Remove vision_dummy demo - no longer used.
Add olfaction model visualization script.
Need to import h5py in olfaction notebook.
Don't need old lpu_parser in intro demo anymore.
lpu_rev_test.py no longer needed.